Porcelain vs. Ceramic Tile Is There a difference?

One of the things we are frequently asked about while helping cli­ents select flooring and countertop materials for kitchens and baths is the difference between por­ce­lain and ceramic tile.

People have a sense that ceramic and por­ce­lain tiles are different, and that por­ce­lain tile is somehow the better of the two but they're not sure how they are different or why por­ce­lain is better. [1]

The confusion is intentional. If you carefully examine the source of all the myths surrounding por­ce­lain tile, you will find that almost all originate with tile sellers.

Companies that sell tile want you to believe that you really must have por­ce­lain tile in your home because it is so much better than ordinary ceramic.

But, the real motive is monetary. Porcelain tile is usually the more expensive tile and if they can persuade you that you can't possible get along with the less expensive ceramic tile, they make more money.

We don't sell tile. We are tile buyers. We use tile, but we don't make it and we don't sell it.

Several years ago we started wondering what additional features we were buying for the extra money we were spending on por­ce­lain tile. What we found out surprised us, and will very likely surprise you.

So, exactly what is por­ce­lain tile, and is it really better than ceramic tile? Let's see if we can de-mystify por­ce­lain tile a little.

Let's start with this simple, basic fact:

Porcelain and Ceramic Are Not Different Kinds of Tile – They Are Both Ceramic Tile

Bet your tile seller did not tell you that little fact. But, it's absolutely true.

Ceramic is a word derived from the ancient Greek "keramos" meaning roughly "of fired clay". Porcelain is just one of many varieties of ceramic made by firing clay in a kiln.

Ceramic technology is very old. It pre-dates modern humans. The oldest ceramic object discovered so far is a statue called the Venus of Dolni Vestonice, made by a Cro-Magnon artisan some 26,000 years ago in what is now the Czech Republic.

The recipe has not changed over the millennia. All ceramic, including por­ce­lain, is still made out of clay, some additives such as feldspar, bentonite, and quartz; and water.

But, not just any old backyard clay will do. China clay, suitable for making ceramic tile, contains a high proportion of a mineral called kao­li­nite, and, for that reason is often called kao­lin clay or just kao­lin.

The European Definition of Porcelain

Kao­lin results from the chemical decay of silica minerals, mostly feldspar.

Pure kaol­i­nite is bright white but oure kaol­i­note is very rare. Most deposits of tile clay are mixes of kaol­i­nite and other minerals such as alumina, silica, mica, quartz, and, especially, iron oxide.

The Clay Firing Process

The chemical and mechanical changes that occur during the firing process are enormously complex, and even after 10,000 years for firing clay, not completely understood. A lot of tile making is still art, using trial and error rather than science.

A bisque is fired in four stages. The temperature of the kiln is slowly increased until the desired firing temperature is reached, then the tile is slowly cooled until it reaches room temperature. The higher the target firing temperature and the longer the bisque is held at that temperature the harder and more water-resistant the resulting tile.

Stage 1. Drying: (up to 480° F). Residual water removed. Temp­era­ture is raised slowly to prevent explosive vaporization.

Stage 2: Dehydroxylation & Ox­ida­tion: (480° to 930° F) Chem­ic­ally bonded or "lattice" water evaporated (dehydroxylation), organic matter burns off (oxidation).

Stage 3: Vitrification: (930° to 2,700° F) kaol­i­nite particles crystallize through several intermediate states as the temperature rises, finally transforming into mullite and cristobalite — elements that give tile its strength and rigidity — while glassy components of the bisque melt and flow into the spaces between the clay particles.

Stage 4: Cooling: (2,700° to room temperature) Tile is allowed to return to room temperature slowly to prevent cracking.

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Iron, which is plentiful in the earth's crust, is the main source of the orange, brown, and terra-cotta colors of most china clays.

The term "por­ce­lain" has been used in Italy at least since at least the late 13th century [2] to describe ceramic tile made of white clay.

To medieval Italians, or so the story goes, the resulting ceramic products had the color and luster of the much-admired shell of the porcellana cowrie. So, that's what they called it: porcellana. [3] The French corrupted the word to "por­ce­lain" and we adopted (the French say "purloined") the French word.

The clay and additives are mixed with water to produce a paste (or slip) which is formed into a biscuit (or bisque) — the body of the tile — and heated to a very high temperature (usually between 2,000° and 2,500° Fahrenheit) in a kiln using a process first discovered by early humans about 10,000 years ago.

All clay tile is fired the same way. Folk wisdom has it that por­ce­lain tile is better because it contains a higher proportion of kaol­i­nite than red or terra-cotta tile.

But, in fact, it's not the proportion of kaol­i­nite in the mix [4] that makes a better tile but the proportion that is chemically trans­formed by firing the tile.

Firing drives out water, hardens the clay and fuses the clay particles together – a process known as sintering[5]

It also changes the silica in the mix to a crude glass which flows into the gaps between the clay particles, sealing them up. This process is known as vitrification[6]

If all of the gaps in the tile are filled with glass, the tile is considered highly vitrified and becomes essentially waterproof.

How much of the mix is vitrified depends on how long and how hot the bisque is fired. If fired for a long time at a high temperature more water is driven out and more sintering and vitrification occurs resulting in a denser, harder tile more resistant to water absorption.

Light-colored clays can be hard-fired, as can more common red, brown, or terra-cotta clays. The firing process is color-blind. The color of the clay makes absolutely no difference.

So, our first definition of por­ce­lain — the traditional or European definition — is simply

A tile made from white or light-colored clay.

That's it. There is no difference between por­ce­lain and other types of ceramic tile in the European tradition other than the color of the bisque.

The tile may be hard, or not; fired for a long time, or not, and very fused and highly vitrified, or not. As used in this traditional sense, the term por­ce­lain tells us nothing about the quality of the tile. It tells us only that the tile is made out of light-colored, porcellana clay rather than red or brown terra-cotta clay.

A number of widespread myths have grown up around por­ce­lain tile over the years — most of them utter nonsense. Here are a few of our all-time favorite goofy fables about por­ce­lain tile.

Porcelain glaze has a depth and luster not available on ordinary ceramic tile.

The truth is that glaze is deep and lustrous if the manufacturer applies a thick coat of lustrous glaze.

It makes no difference what it is applied to. Glaze can be used to decorate and protect clay tile, steel, iron, pottery, china, even concrete — in fact, just about any material that can withstand the firing temperature.

The notion that por­ce­lain glaze is somehow deeper and more lustrous is pure fiction.

Porcelain tile is made from a special "refined" por­ce­lain clay.

Horse apples!

Of course, each manufacturer has its own "secret formula" for tile but there is no special clay mixture used to make por­ce­lain tile. In fact, there are no "composition standards"for ceramic tile, period. But, this fact has not slowed the many "composition" myths surrounding por­ce­lain tile. These suggest that the clay formula used in por­ce­lain has some special or unique properties.

Here are some of our favorite variations found on the web from folks who really should know better:

HouseandHome.com: “Porcelain tile is … made from a much finer clay than ceramic, composing kao­linitic minerals, quartz, and feldspar, covered by spray and shaped by dry pressing the clay dust to form a ceramic material that is then fired at higher temperatures than ceramic.”

HomeAdditionsPlus.com: “The only difference between por­ce­lain tile and regular ceramic tile is that the clay used in por­ce­lain tile is more highly refined and purified. …”

World Floor Covering Association: Porcelain tiles “ are made up of a sand-like material".” (Evi­dently blissfully unaware that firing a “sand-like material” produces glass, not ceramic tile.)

It's all total balderdash, there is no special clay formula for por­ce­lain tile.

The installation of por­ce­lain tile requires special tools.

Porcelain requires the same tools as any ceramic tile. No "special tools" are required to install por­ce­lain tile as suggested by some "experts"(See e.g. FastFloors.com). All the tools required are already in any tile setter's toolbox.

Highly vitrified tile will take more time to install. It is very hard, saws more slowly, and chews up sawblades more quickly. And, because it is less porous, it accepts thin-set adhesive less readily.

Experienced tile-setters will use a special extra sticky adhesive on very hard tiles. But, again, this is true of all highly very hard tiles, not just those that the manufacturer has chosen to call por­ce­lain. The additional time is not significant and should add very little to the cost of installation.

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So, if it's that easy, why is there so much confusion about por­ce­lain tile?

Very briefly, here's what happened: Columbus discovered the Americas; Washington, Franklin, and Adams engineered independence from King George III of England; Americans began making their own ceramic tile and in the process thoroughly muddled the definition of por­ce­lain.

The American Definition of Porcelain

The American definition of por­ce­lain is much newer and very different — almost the exact opposite. It results from the particular American experience with fired clay products.

In the U.S. there are three separate and distinct ceramics in­dus­tries:[7] ceramic tile, dishware & pottery, and sanitaryware.

There is almost no overlap. Makers of fine china do not produce toilets, toilet manufacturers do not make floor tile and floor tile companies do not manufacture vases or those cute little figurines for your curio cabinet.

This is a little curious because they all use basically the same raw materials and roughly the same manufacturing process: a clay paste is shaped into a product — a salad bowl, sink, vase, floor tile, etc. — and then fired at high temperature to harden the clay. Then the product is covered with an impenetrable, baked-on, glass coating.

In the early days, American tile companies rarely made traditional por­ce­lain tile. If someone wanted por­ce­lain, it was imported from Europe.

But, the other clay industries adopted traditional Euro­pean por­ce­lain very quickly, and their products soon earned a reputation for being of exceptional quality.

By 1917 Len­ox had replaced Euro­pean manufacturers such as Spode and Wedg­wood as the purveyor of fine china to the White House. Koh­ler and Amer­ican Stand­ard had firmly established the "Amer­ican stand­ard" for nearly faultless por­ce­lain bathroom fixtures as early as the 1890s.

By the time American tile makers needed a word to describe their better quality ceramic tile, "por­ce­lain" was available and already well-established in the minds of the buying public as describing ceramic products of exceptional quality.

So, they borrowed it, and por­ce­lain, over time, became the term reserved for better quality tile.

There is some evidence that American por­ce­lain tile followed the Euro­pean practice of using only light-colored clay for a few years. But, after a while, this limitation began to give way so that by the 1970s the term was applied to any high-quality tile no matter the color of the clay.

Today, American por­ce­lain may have a tile body that is red, tan, white, brown — any color so long as the tile is of good quality tile. And that's our second definition of por­ce­lain:

Tile that is considered by its manufacturer to be a superior product.

So, for American tile makers, the defining characteristic of por­ce­lain tile is the quality of the tile, not its color. The tile may be of any color — red, white, buff, gray, terra-cotta, black, blue, or indigo — but it must be a tile of good quality.

Rectified Tile

When the guy at the tile store tells you that the tile you are looking at is more expensive because it has been rectified, it sounds vaguely ominous — like someone's been naughty and got sent to the principal's office. Just what does he mean?

Tile that is fired at a very high temperature loses most of its moisture, causing the raw tile bisque to shrink.

Shrinkage is very controlled these days so that the finished size or "caliber" of the resulting tiles is very uniform — usually less than 1/16th of an inch difference from tile to tile.

But, if the tile has to all be exactly the same size, it is "rectified" by cutting all the tiles to exactly the same size on a saw or grinder. This extra step adds a little to the price of the tile.

Rectified tile is for special applications and is just not needed for most home uses, so don't pay for it unless your tile installer insists you actually need it.

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Full-Bodied & Through-Bodied Tile

The problem with the American definition is that it conflicts with the general public perception of por­ce­lain.

While most people don't know very much about por­ce­lain, they are pretty sure that it is supposed to be a white- or light-bodied tile, not red, brown, or terracotta.

Con­se­quent­ly, tile sellers often meet with a lot of skepticism when they try to sell red-brown clay tiles as por­ce­lain.

To overcome this problem, American tile manufacturers have come up with a clever distinction between red or brown and light-bodied por­ce­lain tile. Light-bodied tile is "full-bodied" or "through-bodied" por­ce­lain.

So, the salesman can tell you, with an absolutely straight face, that the wine red ceramic tile you are looking at is actually por­ce­lain, it's just not full-bodied por­ce­lain — implying that you must be an unwashed country bumpkin for not knowing the difference.

Irreconcilable Differences

So, we now have two almost opposite and conflicting definitions of por­ce­lain:

So, if the tile store clerk claims that the tile you are looking at is "por­ce­lain", what does he mean? Is it a high-quality tile, or a light-bodied tile? Both?

When you buy a tile labeled "por­ce­lain", just what are you buying?

Testing & Rating Ceramic Tile

Although some tile "experts" expound at length on the "special" and "unique" properties of the clay mix used to make por­ce­lain tile, there is, in fact, no such special clay mix (See Some Silly Porcelain Myths).

There are no composition standards at all for general-use clay tile.

No one cares about the type or color of the clay used or just how much or how little kaol­i­nite, or feldspar, or quartz sand, etc. is included in the mixture.

Manufacturers can make tile out of any composition and color of clay, and include any additive that they think will produce a better tile. The standards don't care one way or another.

Nor is anyone particularly concerned about how the tile is made. There are no process standards for general-use tile.

Any manufacturing method that will work is just fine. The tile can be shaped by machine, or by hand. It can be extruded, pressed, or globbed into a form. The tile can be fired using an old tunnel kiln, or the newer roller-kilns, or a kiln at the local high school.

With rare exception — for special purpose tiles — the heat-shield tiles on the space shuttle, for example, the standards simply don't give a hoot how a tile is made.

PEI Wear Resistance Ratings
Group I
The softest tile. Suitable for walls and hobby crafts only, no floors.

Group II
Residential use in low foot traffic areas. In rooms where there is usually no through traffic, this tile might work. But, in kitchens, where there is often a lot of through traffic, this tile would be suspect.

Group III
All residential, medium commercial, normal foot traffic (interior only). Any bathroom or kitchen, mudroom, laundry room or hallway but nothing outside.

Group IV
Heavy commercial. Any interior use. Suited for residential floors that get a lot of use and for exterior applications where there is not a hard freeze in winter.

Group V
The most wear-resistant tile. Extra heavy, high traffic, commercial (interior or exterior use).

What the standards do care about and do test extensively is how well the tile performs.

Standards used to rate fired clay tiles are all performance standards.

If a tile performs to a certain standard, it gets rated for that standard no matter what it is made of, how it was made, or what color it is.

Ceramic Tile Performance Standards

Ceramic tile is subjected to a great many tests. It is tested for slipperiness; resistance to cold, heat, and chemical damage; breaking strength, and stain resistance, among others — and we will touch on a few more of these tests in Part 2 of this article.

But, the two most widely used — and certainly the most widely quoted and misquoted — tests of fired clay tile are the wear resistance and water absorption tests.

The wear resistance test, developed by the Porcelain Enamel Institute (PEI) reveals how well the tile resists damage from foot traffic. The absorption test, supervised by the American National Standards Institute (ANSI), looks at how waterproof a tile is.

These distinctions do not necessarily make one tile better or worse than another, they merely help determine where and how a tile may be used.

A tile that absorbs a lot of water should not be used outside where it freezes because the freeze-thaw cycle will crack the tile. But, it may be quite suitable as wall tile around a fireplace where water absorption matters not at all.

A tile that is not very hard may not work for floors or countertops but will be just fine for walls, backsplashes, and hobby crafts where surface wear is not an issue.

ANSI Water Resistance Ratings
Water absorption of more than 7.0% by volume.
Tile for non-wet areas. Around fire­places, for example. Typically intended for walls, hobby, and crafts use.

Water absorption of more than 3.0% but not more than 7.0%.
Tile for areas that may get wet on occasion but are unlikely to see constant or standing water. Back­spla­shes or countertops, for example.

Water absorption of more than 0.5% but not more than 3.0%.
Virtually any indoor application including shower walls and floors. Outdoors in areas that do not freeze. (Although some Vitreous tiles will pass the frost test, and can be used outdoors. The frost test is discussed later in this article.)

Water absorption of 0.5 percent or less.
Any indoor or outdoor application.

PEI Rating: Resistance to Surface Wear

The rating developed by The Porcelain Enamel Institute is a test of surface wear resistance. It involves applying steel ball bearings and aluminum oxide (the grit used in sandpaper) to a tile. A tile is scored by how quickly it shows visible signs of wear.

The classification is colloquially known as the PEI Scale or "Wear Scale". The classifications are numeric. The numbers define the suitable uses for the tile. The higher the number, the more wear-resistant the tile and the more places it can be used.

(View the PEI Wear Resistance Ratings.)

ANSI Rating: Resistance to Water Penetration

The rating developed by The American National Standards Institute (ANSI) is a test of resistance to permeability by water. It consists of weighing the tile, then boiling it for five hours. The tile is then soaked in cold water for another 24 hours. It is then measured again to find its gain in weight from the original dry state.

Any weight gain indicates water absorbed by the tile. The result is stated as a percent of change from its original dry weight. [8] Four ratings resulted from ANSI's studies of clay-fired tiles. These are, from lowest to highest: Non-Vitreous, Semi-Vitreous, Vitreous and Impervious.

Non-vitreous tile is the most permeable. Semi-vitreous is slightly less so because more of the tiny spaces between clay particles have been filled with glass. A Vitreous tile is even less permeable.

An Impervious tile is the least porous — in fact, it is essentially waterproof — but instead of calling it super-vitreous or waterproof, the creators of the test settled on Impervious.

Waterproof would actually be the more accurate term. Impervious (in regular English as opposed to engineer-speak) means more than just waterproof. It also means "impregnable" or "invulnerable".

Impervious tile is neither impregnable nor invulnerable.

Hit it with a hammer, it will break. So, when you see or hear the word impervious applied to tile, think "waterproof". That way your mind won't be fooled into thinking the tile is something it's not.

(View the ANSI Water Re­sis­tance Ratings.)

The ANSI-PEI Relationshiip

There is a relation between the two ratings, at least for unglazed tiles such as quarry or saltillo tiles.

Tile that is harder and thus more wear-resistant is a tile that was fired longer or at a higher temperature or both. This is also the tile that tends to be more resistant to water penetration.

With glazed tiles, however, the relationship breaks down. If a tile has a surface glaze, the glaze becomes the wear layer, and it is the glaze that is subjected to the PEI wear test, not the body of the tile beneath the glaze.

A very hard glaze can be applied to a very soft tile, so, with glazed tiles, it is possible to achieve a high wear rating with a low water-resistance score. (More about tile glaze below.)

The ANSI Definition of Porcelain Tile

We already have two different definitions of por­ce­lain tile: the traditional or Euro­pean definition, and the newer American definition. And, just to make things even more fun, there is yet a third generally accepted definition: the ANSI definition of por­ce­lain.

In 1988, under pressure from American tile manufacturers and seeking to clarify once and for all time the burning international issue of what is a por­ce­lain tile, the American National Standards Institute (ANSI – the same guys that developed the water-resistance test) adopted what it hoped would become the only official U.S. definition of por­ce­lain tile, assigning, they hoped, the traditional color-based definition to oblivion.

In its American National Standard Specifications for Ceramic Tile (ANSI A137.1) ANSI declared a tile to be por­ce­lain only if it is

"…generally made by the dust-pressed method of a composition resulting in a tile that is dense, Impervious, fine-grained, and smooth with a sharply formed face."

While this is definitely written in engineer-speak, what it does is define two different tests for identifying a por­ce­lain tile.

The first is the same performance test used to rate all tile. A por­ce­lain tile must perform at the highest, Impervious, standard in the ANSI water-absorption test (See above). The second is something rarer — a "process" test. To be called por­ce­lain, tile must be made by the "dust press" method or process.

How Tile is Shaped

Tile can be shaped using any method from hand globbing clay into a form at a local artisan tile shop to the use of roller mills and high pressure presses. For mass production, nowever, the usual methods are pressing and rolling.

Raw floor tiles emerge fully formed from a hydraulic press.

Only a small amount of water in the bisque is needed for the clay to bond under pressure.

These will be sprayed several times with a glaze mixture, then sent to a kiln to bake up to 24 hours at temperatures approaching 2,000°F.

An extrusion mill is a more common process for forming tile. Clay is forced through a die to form a ribbon, then the ribbon is cut into individual tiles.

The process requires more water than the dust press method but forms the tile much faster and is less expensive.

This mill is more efficient than most. It forms two ribbons of bisque at the same time.

The dust or "dry" press method is a process for manufacturing tile that has very little to do with tile quality. It is mostly a measure for controlling tile shrinkage.

All fired clay tile shrinks when it is fired and water in the biscuit evaporates. If there is a lot of water, there is a lot of evaporation and, consequently, a lot of shrinkage. Controlling shrinkage is important if the resulting tiles are to be the same finished size, or "caliber".

Encaustic Tile


Encaustic tiles are ceramic tiles in which the pattern or figure on the surface is not a product of the glaze but of different colors of clay inlaid into indentations in the body of the tile.

The inlays are typically 1/8 to 1/4 inch thick, and they may be composed of as many as six colors. Because of its thickness, the inlaid pattern remains as the tile is worn down over time, which makes the tiles preferred for public buildings that are heavily trafficked.

Popular in medieval times and used in a number of Gothic cathedrals in Europe until the 16th century, encaustic tiles were revived during the Victorian era and mass-produced by companies in the United States such as the American Encaustic Tiling Company of Zanesville, Ohio, which was active until 1935.


Min­ton, Hol­lins and Comp­any in Stoke-Up­on-Trent, Staf­ford­shire, Eng­land, produced the encaustic tile, pictured at top, installed in the U.S. Cap­i­tol building when it was enlarged in 1856.

Its successor company, H & R John­son Tiles Ltd. has revived its production of encaustic tile for the current restoration of the Smith­son­i­an In­sti­tu­tion as well as the U.S. Cap­i­tol.

Cra­ven Dun­nill-Jack­field of Shrop­shire also revived its production of encaustic tiles in 2000 in its old tile works, now a part of the Jack­field Tile Mus­eum.

It now produces encaustic tile for projects throughout the world, including restoration of the Eng­lish Hous­es of Parl­i­a­ment.

For a video on the manufacture of encaustic tile using Vic­tor­ian methods and machinery, see En­caus­tic Vict­or­ian Tile Man­u­fact­ur­ing.

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Caliber is important. If tiles vary too much in face dimensions they are much harder to set in a pleasing, un­iform manner and often require a wide grout line to mask the unevenness of the tile. Tiles that are very similar in finished size can be set with a narrower grout line.

The dust press method does not actually use dust to make a bisque. A little water — about 6% — is required to dampen the clay mix which is then pressed into shape. The pressure helps the clay particles stick together so the bisque retains its shape. With so little water in the mix, shrinkage is minimal and the resulting tiles are likely to be of a more uniform size.

The other, more widely used method, is the extrusion pro­cess in which slightly wetter clay is fed into a mold that extrudes a ribbon of biscuit that is then sliced into individual tiles. In the past, shrinkage was a little less controlled using this method.

However, as we know, pro­cess standards are very rare in the tile world, and almost unheard of when rating general use tile. Accordingly, this one did not last long.

Since the standard was first issued, tile chemists and materials engineers have made enormous strides in controlling shrinkage using the extrusion process — primarily through additives, such as calcium lignosulfonate, that make water "wetter". [9]

Wetter water means less water is needed in the paste. As a result, extrusion now produces tile of very uniform caliber.

Recognizing this change, ANSI dropped the requirement that por­ce­lain be made by the dust press process in its later versions of A137.1. Any manufacturing process may now be used to make por­ce­lain tile as long as the tile rates Impervious.

The effect is that "por­ce­lain" under the ANSI standard has become just an alternate word for "Impervious", which, as we noted earlier, is just engineer-speak for "waterproof". If a tile meets the criteria for being rated Impervious to water penetration, it may, according to ANSI, be called por­ce­lain.

American tile manufacturers welcomed the new standard with warm applause and great enthusiasm. Euro­pean, South American, and most Asian tile makers greeted it with a great big yawn and cheerfully ignored it.

On some tile, a thin additional layer or “slip” of clay mix called “engobe” is applied to the tile body. Engobe acts like a primer for the finish glaze coat.

It is a usually light fine-grained clay that may be colored with various metal oxides to more or less match the final glaze color. This helps intensify the color of the glaze and keeps a dark tile body from showing through a lighter glaze.

It is also used to fill in any minor imperfections in the tile body so the finished glaze is smoother. Very glossy tiles almost always include an engobe layer.

After the glaze is fired, a tile can be given a little polish to improve its shine. Some tiles are highly polished, a delicate operation since it is easy to cut completely through the glaze and expose the softer engobe layer which can scratch and stain easily.

High gloss tile should always be tested for stain and scratch resistance before buying.

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Imported tile is generally rated under a different set of standards published by the International Standards Organization (ISO), which had until recently, very wisely, stayed far away from the fray over what is or is not por­ce­lain tile

Consequently, imported tiles were free to adhere to the Euro­pean definition that declared tile to be por­ce­lain if made with light-colored clay.

The ISO Definition of Porcelain Tile

But, not having an "official" definition of por­ce­lain caused problems for the ISO.

The U.S. market for ceramic tile is massive — about equal to the entire continent of Europe, so most foreign tile manufacturers want to export to the U.S. But, in order to get an "official" por­ce­lain designation for their qualifying tile, they needed to be certified by ANSI.

This started costing ISO customers as more manufactures switched to ANSI for tile certification.

In 2012 the ISO caved in. The standard that defines and classifies ceramic tile (ISO 13006) was revised to define por­ce­lain tile as tile that is

fully vitrified tile with water absorption coefficient less than or equal to a mass fraction of 0.5%…

which is essentially the ANSI definition — a tile may be called por­ce­lain if it absorbs less than .05% water by volume, or is, in other words, rated Impervious in the ANSI water absorption test.

(Actually, the ISO has its own slightly different, somewhat less stringent test — why let the ANSI guys have all the glory, right?)

So, it was a long road but everyone finally agrees that the old color-based definition of por­ce­lain is extinct. The term por­ce­lain will be reserved only for high-quality tile in the American tradition that meets either the ANSI or ISO standard for Impervious tile. Right?

Not a chance! Sorry! Wish it were that easy.

If some law required ceramic tile to be graded, then a standard defining por­ce­lain would eliminate any issue about what is or is not por­ce­lain tile. The question would then be which of the competing standards to use.

But, both ANSI and ISO standards are completely voluntary.

No tile maker is bound to observe them. And, a great many don't. Ceramic tile may legitimately be called por­ce­lain even if it is not "Impervious" as long as it does not claim to meet the ANSI (or ISO) standard for por­ce­lain.

So, where does that leave us?

Unfortunately, just about where we started. The attempt by the standards organizations to create a universal standard for por­ce­lain has really had little effect except to make a confusing situation even more confusing.

Both the ANSI and ISO standards are less than 50 years old in an industry that was already many thousands of years old before Rome was an Empire.

Many tile makers choose to ignore these new standards, especially traditionalist manufacturers that still adhere to the older color-based, definition of por­celain tile.

And, while American tile manufacturers have tried mightily to get the ANSI definition enacted into federal law, our Right Honorable Congress-Persons have so far been busy with much weightier matters — primarily getting re-elected and calling each other names. [10]

As the situation now stands, the use of the word por­ce­lain to describe ceramic tile has been left almost entirely to the discretion of individual tile manufacturers. Whe­ther they have their tiles tested and certified under either ANSI or the ISO standard as por­ce­lain, and how and when they use the term to describe their tile is completely up to them.

As a result, when the word por­ce­lain appears on a box of tile it is often not possible to discover what it actually means. It may legitimately mean …

A high-quality tile of any color,


A light-bodied tile of any quality,


A tile rated "Impervious" under ANSI standard A137.1


A tile meeting the definition of por­ce­lain under ISO standard 13006.

So, does the word "por­ce­lain" printed on the box actually help you select a suitable tile?

It tells you nothing about the color of the tile — por­ce­lain in the American tradition can be of any color.

It does not reveal anything about the quality of the tile — por­ce­lain in the Euro­pean tradition may be of any quality.

In fact, it does not tell you much of anything useful about the tile. The term "por­ce­lain" is so ambiguous as to be useless. If the tile meets any of the many definitions of por­ce­lain, and its manufacturer elects to call it por­ce­lain, then it is — legitimately — por­ce­lain.

Our best advice: ignore the term por­ce­lain altogether when shopping for clay-fired tiles. Disregarding the dubious distinction between por­ce­lain and other ceramic tile actually makes choosing tile much, much easier and a lot less confusing.

To find out how to actually buy the right ceramic tile for your project, Continue to the next section: How to Choose Ceramic Tile.

[1] This confusion is not new. Over 100 years ago William Burton was already complaining that the word por­ce­lain was being applied to such diverse materials that it had lost all meaning. See: Burton, William, Porcelain, Its Nature, Art and Manufacture, B. T. Batsford Ltd., London 1906, pp. 47—48. Available online and as an e-book, courtesy Google Books.
[2] The Venetian explorer, Marco Polo is reputed to have been the first to use the word porcellana in print to describe ceramic pottery c. 1298.
[3] No one has yet explained why the shell of the porcellana cowrie was so admired. It looks more or less like every other sea shell.
[4] Pure kao­lin actually produces a relatively fragile and brittle tile. Kaolin needs to be combined with other clays, such as ball clay.to improve elasticity and strength. Ball clays typically contain mica and quartz as well as some kao­lin. They are fine-grained and plastic in nature which makes them ideal for modifying the very brittle pure kaol­i­nite. Ball clay deposits are relatively rare, mined primarily in the Eastern United States and in Devon and Dorset in Southwest England.
[5] Sintering is normally defined as a process of making a powdered material coalesce into a solid mass by heating it but not liquifying it. The clay particles in the bisque do not melt but do get hot enough to stick together. In metallurgy, it is a cheap and fast way of forming metal without having to cast it in liquid form. The resulting product is not nearly as strong but so-called "clinker casting" is suitable for things that do not have to be particularly strong such as cabinet knobs and light-duty hinges.
[6] The process of transforming a clay paste into ceramic tile through firing is one of the most complex in industrial chemistry, involving a number of what chemists call "structural transformations" of kaol­i­nite and silica materials. Kao­lin becomes metakao­lin at about 1,100° F begins to form a material called mullite at about 2,000°. As the temperature continues to rise, silica in the paste is transformed into molten glass. Mullite and glass in its various forms are the major constituents of fired ceramics. The Kao­lin clay transformed into mullite gives the tile its characteristic strength, structure, and shape while the glass helps it resist water penetration.
[7] We have excluded brick making from the roundup since bricks are seldom glazed.
[8] The formula is (Ws - Wd )/Wd x 100 where Ws is the saturated weight and Wd the dry weight of the tile. For example, A tile that weighs 4 oz. dry and 4.25 oz. saturated has an absorption rate of ( 4.25 - 4 )/4 x 100 or 6.25% and would be classified as Semi-Vitreous tile.
[9] Everyone knows that water is composed of one oxygen and two hydrogen atoms tightly bound together. But, hydrogen atoms in the molecule also bind weakly to oxygen atoms in neighboring molecules. This weak bond tends to keep water molecules together, which is why water tends to form drops.
Any additive that weakens this oxygen-hydrogen bond is called a surfactant and has the effect of making water "wetter". Common household surfactants are soap, dishwashing liquid, shampoo, and toothpaste.
Wetter water reacts with its environment more readily than untreated water, which is why soapy water cleans better than plain water.
Wetter water also cools automotive engines better, is more quickly and thoroughly absorbed into soil (reducing the amount needed for irrigation), puts out fires faster (the foam in many fire extinguishers is just wetter water), and is thought by some to be healthier than regular water because it "improves hydration at the cellular level" (a notion that has never been proven, by the way).
[10] "In my many years I have come to the conclusion that one useless man is a shame, two a law firm, and three or more a Congress."
John Adams, second President of the United States, circa 1802.

Rev. 05/31/21